Devil's advocate here; but the laws listed are a combination of "after-the-fact" and "not really enforceable" with respect to the violent crime scene.

"It's illegal to make and sell guns" is enforceable far in advance of the violent crime scene. It has the secondary effect too of having a society where said offender is less likely to be familiar with or unafraid of firearms and seek to acquire them (or be able to effectively deploy them) in the first place.